Typically drainage from timber joinery type windows is not specifically allowed for, in that there appear to be no specific design or apparatus that are used. Instead one tries to prevent water or moisture that originates from condensation or rainfall or anywhere, from entering or passing through a window. This is currently done by applying various sealing means such as by caulking guns or by installing flexible sealing strips. This drainage problem is especially apparent in Insulated Glass Units or as is commonly referred to as IGU's or as Double Glazing Units, i.e., DGU's whereby there can be fixed sashes or opening sashes.
Problems occur with his type of moisture prevention in window glazing assemblies, in that the flexible seals or strips, break down in sunlight. Also successful sealer installation is dependent on skilled installers and so is often improperly installed causing unintentional leaking into the building and into the internal wall framework.
Various flashings are often used in such situations to prevent entry of moisture in the walls of building but these do not address the problem of moisture of rotting timber sills in that moisture has to pass through any sill to get to the flashing to be directed away. Before moisture gets to the flashing the moisture meets any timber joinery which has no resistance.
Current moisture entry prevention methods are not able to provide a guarantee of weather tightness according to some warranties. This has been a real problem to installers meaning that no warranty has been able to be given to customers which has significantly reduced the desire to double glaze timber joinery windows for better noise and energy efficiency.
Methods of installing double glazing units cause problems for building owners, with a difficult and messy method of window removal caused by needing to remove the putty and the glass to get it out plus there is no guarantee of weather tightness. Such removal often involves glass breakage. This in turn causes there to be more costs to building owners with little incentive to improve current timber joinery which exists for many New Zealand residences.
In this specification unless the contrary is expressly stated, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date, publicly available, known to the public, part of common general knowledge; or known to be relevant to an attempt to solve any problem with which this specification is concerned.